Octave: ismember does not support cell syntax

Replaced by a switch, where the relevant syntax IS supported
by both MATLAB and Octave 3.6.4
Octave: nargout workaround for Octave

In Octave 3.6.4, nargout cannot handle function handles, so using strings.
Moreover, it seems to fail for nested functions, so it makes the
liberal use of the number of output arguments going FUBAR.

As a workaround, we now just try the nargout approach, if it fails,
we fall back to the default one: 2 outputs and issue a warning
Merge branch 'fix308': works around #308